1. Field of the Invention
The present invention relates to a hydraulic transaxle adaptable to a vehicle, e.g., a lawn mower, equipped with a hydraulic actuator, e.g., a device for lifting a mower deck.
2. Related Art
A lawn mower is equipped with a lift mechanism for raising and lowering a mower deck. A typical lift mechanism is manually operated to adjust a height of a mower deck. Further, there is a conventional lawn mower equipped with an automatic mower-deck lifting unit, as disclosed by U.S. Pat. No. 7,730,705 B2. This unit integrally includes a hydraulic actuator (hydraulic cylinder) for raising and lowering a mower deck, a hydraulic pump for supplying fluid to the hydraulic actuator, and an electric motor for driving the hydraulic pump. This unit is mounted on a vehicle frame of the lawn mower, and a piston rod of the hydraulic actuator is connected to a linkage suspending the mower deck.
Further, there is a conventional hydraulic zero-turn vehicle driving system, as disclosed by US 2011/0162355 A1. This system includes right and left hydraulic transaxles carrying respective right and left axles. The right and left hydraulic transaxles include respective transaxle housings separated from each other, and each of the transaxle housings incorporates a hydrostatic stepless transmission (hereinafter, HST) for driving the corresponding axle. This reference discloses an embodiment in which a charge pump in one transaxle housing supplies fluid from a fluid sump in this transaxle housing to the HST in the other transaxle housing.
Further, there is a conventional hydraulic transaxle as disclosed by JP H02-51763 U. This hydraulic transaxle includes a transaxle housing that incorporates a differential unit supporting right and left axles, and an HST for driving the differential unit. This transaxle housing further incorporates a trochoidal pump serving as a charge pump for supplying fluid from a fluid sump in the transaxle housing to the HST, and incorporates another trochoidal pump for supplying fluid to a hydraulic actuator disposed outside of the transaxle housing to lift a mower deck so as to effect radiating heat from fluid when flowing in a pipe between the transaxle housings.
If an electric-hydraulic mower-deck lifting unit such as disclosed by U.S. Pat. No. 7,730,705 B2 were equipped on a lawn mower with a hydraulic zero-turn vehicle driving system including right and left hydraulic transaxles such as disclosed by US 2011/0162355 A1, the mower-deck lifting unit would occupy a large space outside of the right and left transaxles so as to provide an insufficient ground clearance to the lawn mower.
JP H02-51763 U suggests that a hydraulic transaxle incorporates a hydraulic pump for supplying fluid to a hydraulic actuator for lifting a mower deck. However, this transaxle, including the differential unit supporting the right and left axles, is not a zero-turn vehicle driving system including right and left separate transaxles. The charge pump of this transaxle supplies fluid to the HST in its own transaxle housing, and cannot supply fluid outward from the transaxle housing.
As a result, there is no conventional hydraulic transaxle adaptable to a hydraulic zero-turn vehicle driving system for a vehicle, e.g., a lawn mower, which is available to effectively radiate heat from fluid, and which is also available to operate a hydraulic actuator disposed outside of the hydraulic transaxle, e.g., a hydraulic actuator for raising and lowering a mower deck.